Process for high purity hexane and production thereof

ABSTRACT

The invention relates to the production of High purity n-hexane from low value stream such as raffinate from benzene extraction unit in crude oil refineries employing extractive distillation. The present invention further related to an extractive distillation employing an organic solvent having comparable or same Hansen dispersive force parameter (δ d ) of that of the key component of to be separated through extractive distillation. The present invention is useful for separating and isolating pure cyclohexane, pure methylcyclopentane and pure iso-heptane along with the pure n-hexane.

FIELD OF THE INVENTION

The invention relates to the production of High purity hexane from lowvalue stream such as raffinate from benzene extraction unit in crude oilrefineries employing extractive distillation.

BACKGROUND OF THE INVENTION

The naphtha solvents have different applications in chemical andpetrochemical industries such as solvents for extraction of vegetableoil, polymerization process and for cleanup and maintenance operations.Naphtha solvents used in food processing to extract selective ingredientfrom a raw material, should follow the criteria set for toxicologicalnorms and in petrochemical process. High purity hexane is naphthasolvent in the range of 65° C. to 70° C. with aromatics, mainly benzeneknown as High purity hexane widely used in polymerization and foodindustry.

Several processes such as catalytic hydrogenation, adsorptivede-aromatization, catalytic distillation and solvent extraction havebeen currently followed in industry for reduction of benzene in naphthafor the production of food grade hexane.

U.S. Pat. No. 3,505,421 describes a process of hydrogenating benzene inliquid phase by means of molecular hydrogen in the presence of suspendedsolid catalyst. U.S. Pat. No. 5,254,763 also describes a process forselective hydrogenation of benzene using water soluble organo-metallichydrogenation catalyst. This hydrogenation process involves hydrogen atelevated temperature and pressure. The hydrogenation process alsoinvolves the removal of sulfur before the reaction, which makes thisprocess more expensive.

The adsorptive de-aromatization was achieved using activated carbon,alumina, and zeolite materials. U.S. Pat. No. 3,963,934 claims theseparation of aromatics from process streams by use of a molecularsieve. Other U.S. Pat. Nos. 2,728,800; 2,847,485; and 2,856,444describes the use of silica gel for adsorbing aromatics from a processstream, followed by desorption by use of a liquid hydrocarbon. U.S. Pat.No. 5,294,334 describes the process for selectively removing benzenefrom gasoline boiling range process streams using aluminosilicatezeolite material. The catalytic distillation for benzene removal isanother method/technology.

U.S. Pat. No. 7,501,549 claims the reduction in benzene from gasolinecan be achieved by feeding a gasoline fraction with an alcohol and etherto a catalytic distillation column with one reaction zone containing analkylation catalyst. Then the C₆ hydrocarbons are separated from C₇₊hydrocarbons. The catalytic hydrogenation is another method for benzeneremoval where benzene reduction, olefin saturation and sulfur reductionoccurs simultaneously.

U.S. Pat. No. 6,153,805 discloses the catalytic hydrogenation of benzeneto produce cyclohexane in the presence of metal catalyst. US PatentApplication 2002/24395 discloses the production of food grade hexane byhydrogenation, using Ni supported alumina catalyst. U.S. Pat. No.4,428,829 reports the production of food grade hexane by separatingaromatics and non-aromatics from heavy hydrocarbon stream by extractionprocess.

U.S. Pat. No. 5,668,293 discloses the process and catalyst for theproduction of cyclohexane by hydrogenation of benzene, comprising of twosteps: a) gradually introducing the feed of benzene for hydrogenationand a hydrogen-rich gas into a reaction zone containing acyclohexane-rich liquid and a nickel-based catalyst in colloidalsuspension and recovering a gaseous phase containing cyclohexane,hydrogen and benzene; and b) introducing the gaseous phase into areactor operating under hydrogenation conditions and containing at leastone fixed bed of a solid nickel-based hydrogenation catalyst.

Indian patent applications 1224/DEL/1994 & 788/DEL/1994 discloses theseparation of the aromatics and non-aromatics from naphtha and kerosenerange fraction by extraction. The raffinate phase is water washed toremove the solvent carryover. The U.S. patent application 20040182750discloses the process for removal of aromatics from petroleum streamslike naphtha, kerosene and gasoil through extraction by using solventslike NMP, Sulfolane and glycol. In all the above said process, solventis recovered by distillation.

U.S. Pat. No. 3,551,327 discloses a process for recovery of aromaticsfrom vapour to liquid phase i.e. by extractive distillation, further italso focuses on raffinate water wash and recovery of sulfolane fromwater. US patent application 20040182750 discloses a process forextraction of aromatics from petroleum fraction like heavy naphtha,kerosene and gas oil. U.S. Pat. Nos. 3,942,765; 4,314,974 discloses aprocess for the removal of metal ions from aqueous solution by usingsolvent in different type of static mixer and then whole process isconfined to static mixer alone. The processes for producing food gradehexane containing less than 100 ppm benzene is hydrogenation (U.S.patent application 20050224395) and adsorption (U.S. Pat. No.4,567,315).

U.S. Pat. No. 6,048,450 discloses a process for the selective reductionin the content of light unsaturated compounds (that is to say containingat the most six carbon atoms per molecule) including benzene, in ahydrocarbon cut comprising mainly at least 5 carbon atoms per molecule,without any significant loss in the octane number, said processcomprising passing said cut into a distillation zone associated with ahydrogenation reaction zone, followed by passing part of the effluentfrom the distillation zone comprising mainly C₅-C₆ hydrocarbons, that isto say containing 5 and/or 6 carbon atoms per molecule into a zone forthe isomerization of paraffins in the presence of an isomerizationcatalyst, to obtain an isomerate containing an increased concentrationof branched hydrocarbons.

US20140353216 discloses a column for consecutive extractivedistillations, in particular of crude hydrocarbon mixes comprisingaromatic, naphthene and paraffin hydrocarbons. It also discloses themethods for separating and recovering the components of a crudehydrocarbon mix comprising aromatic, naphthene and paraffin hydrocarbonsby consecutive extractive distillations.

All the above discussed prior arts need the refineries, which areproducing food grade hexane by solvent extraction process, need to putup separate unit to employ these processes which is cost intensive.

Specifications for food grade hexane with respect to benzene content arebecoming stringent day by day. Refineries producing food grade hexane bysolvent extraction process need to switch to alternative processes likecatalytic hydrogenation and adsorption which calls for additionalcapital investment. Thus there is a need for a process for production ofHigh purity hexane employing extractive distillation using solventhaving similar dispersive force parameter to that of component.

OBJECTIVES OF THE INVENTION

It is an object of this invention to provide a process for production ofHigh purity hexane.

It is another objective of this invention to provide pure cyclohexane,methylcyclopentane and iso-heptane.

It is another objective of invention of separating n-hexane (alsoreferred as hexane) from other paraffins by extractive distillationemploying an organic solvent having comparable or same Hansen dispersiveforce as that of n-hexane.

SUMMARY OF THE INVENTION

The present invention relates to a process of preparing high purityn-hexane by extractive distillation of a hydrocarbon feedstock, whereinthe extractive distillation is carried out using an organic solventhaving comparable to same Hansen dispersive force parameter (δ_(d)) tohexane.

The present invention further relates to a process for producing puren-hexane, said process comprising:

-   -   (a) subjecting a benzene saturated hydrocarbon stream to        fractional separation at a temperature in range of 65° C. to        100° C. to split the benzene saturated hydrocarbon stream into a        bottom stream comprising a mixture of cyclohexane and        iso-heptane and a top stream comprising a mixture of        methylcyclopentane (MCP) and n-hexane;    -   (b) subjecting the top stream of step (a) to extractive        distillation to obtain n-hexane and methylcyclopentane by using        an organic solvent; and    -   (c) separating pure n-hexane.

The present invention further relates to an apparatus for producing puren-hexane, said apparatus comprising:

-   -   (a) a fractional distillation unit [4] to split a benzene        saturated hydrocarbon stream into a bottom stream comprising        cyclohexane and iso-heptane, and a top stream comprising        methylcyclopentane (MCP) and n-hexane;    -   (b) an extractive distillation column [8] for fractionating the        top stream into an overhead stream rich in n-hexane and a bottom        stream comprising methylcyclopentane and organic solvent;    -   (c) a solvent storage [29] for introducing solvent to the        extractive distillation column [8];    -   (d) a condenser [31] for condensing pure n-hexane stream wherein        a portion of condensed stream is passed to the extractive        distillation column [8] through a conduit [17]; and    -   (e) a conduit [21] for isolating pure n-hexane.

DRAWINGS

FIG. 1 is a diagrammatic representation of apparatus for producing puren-hexane, pure methylcyclopentane, pure cyclohexane and pureiso-heptane.

DESCRIPTION OF THE INVENTION

While the invention is susceptible to various modifications and/oralternative processes and/or compositions, specific embodiment thereofhas been shown by way of example in the drawings and tables and will bedescribed in detail below. It should be understood, however that it isnot intended to limit the invention to the particular processes and/orcompositions disclosed, but on the contrary, the invention is to coverall modifications, equivalents, and alternative falling within thespirit and the scope of the invention as defined by the appended claims.

The tables have been represented where appropriate by conventionalrepresentations showing only those specific details that are pertinentto understanding the embodiments of the present invention so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having benefit of the descriptionherein.

The following description is of exemplary embodiments only and is notintended to limit the scope, applicability or configuration of theinvention in any way. Rather, the following description provides aconvenient illustration for implementing exemplary embodiments of theinvention. Various changes to the described embodiments may be made inthe function and arrangement of the elements described without departingfrom the scope of the invention.

In accordance with this invention, in a process for the simultaneousproduction of cyclohexane, methylcyclopentane and high purity hexanefrom C₆ refinery stream containing 6-7 carbon atoms by employing seriesof processes including fractional distillation, and extractivedistillation using a solvent (also referred to as extractant orentrainer) in extractive distillation unit wherein said solvent is atleast one saturated alcohol selected from the group consisting ofalkanols and cycloalkanols, wherein said alkanols are selected from thegroup comprising of C5 to C9 carbon atoms.

Accordingly, the main embodiment of the present invention relates to aprocess of preparing high purity n-hexane by extractive distillation ofa hydrocarbon feedstock, wherein the extractive distillation is carriedout using an organic solvent having comparable to same Hansen dispersiveforce parameter (δ_(d)) to hexane.

In other embodiment the hydrocarbon feedstock is a light naphthafeedstock comprising C₆ raffinate stream of paraffins andcycloparaffins.

In a preferred embodiment the hydrocarbon feedstock is mixture ofpredominately cyclohexane, methylcyclopentane, n-hexane andiso-heptanes.

In another embodiment, the organic solvent is selected from the groupcomprising of C5-C9 alkanols and C5-C9 cycloalkanols.

In another preferred embodiment, the organic solvent is selected frommonoethylene glycol (MEG), triethylene glycol (TEG), N-methylpyrrolidone (NMP), Sulfolane and dimethyl sulfoxide (DMSO). In mostpreferred embodiment, the organic solvent is selected from monoethyleneglycol (MEG) and triethylene glycol (TEG) with matching Hansensolubility parameter and more preferably the matching dispersive force.

Hansen Solubility Parameter:

Solvents suitable for extractive distillation of compounds of interestwere selected based on Hansen solubility parameter in the presentinvention. When a compound is dissolved in a solvent, intermolecularinteractions develop between molecules, in order to achieve goodsolubility, intermolecular interaction force between the solute andsolvent should be identical or at least comparable. When the non-polarmolecules dissolves in the polar solvent, stronger intermolecular forcedevelop than those in non-polar solutes. The solubility characteristicsof the solvent and solute are based on three parameters which are knownas the Hansen Solubility Parameters. The Hansen Solubility Parametersare the factors that determine which set of molecules will interactstrongly with other molecules. The stronger the interaction, the moresoluble those compounds are expected to be. Hence it is an effectivemethod at determining ideal solvents for given solutions of feed. Thesethree forces are:

1) Energy from dispersion force between molecules (δ_(d))

2) Energy from dipolar inter-molecular forces between molecules (δ_(p))

3) Energy from Hydrogen-bonding between molecules (δ_(h)).

In Table-1, only cyclohexane and MCP have equal dispersion force (8.2 &7.7 respectively) as that of solvents, MEG and TEG (8.3 & 7.8respectively) which is a dominant force for measuring/ensuring goodsolubility compared to dipolar intermolecular force and hydrogenbonding. The other solvent like NMP and sulfolane do not give therequired separation for the High purity hexane because they have higherdispersion force than TEG.

TABLE 1 dispersion dipolar inter- Hydrogen- Substance force (δ_(d))molecular force (δ_(p)) bonding (δ_(p)) MEG 8.3 5.4 12.7 TEG 7.8 6.1 9.1NMP 8.8 6.0 3.5 SULFOLANE 9 7.4 5.3 DMSO 9 8 5 Cyclohexane 8.2 0.0 0.1Methylcyclopentane 7.7 1.7 0.0 Hexane 7.3 0.0 0.0 2,4-Dimethylpentane 70 0

In another preferred embodiment, solvent preferred based on the matchingHansen dispersive force enhances separation factor.

In another preferred embodiment, the enhanced separation factor improvespurity of preferred components namely cyclohexane as well asmethylcyclopentane and thus reduces separation stages.

The present invention is a process for producing high purity hexane aswell as cyclohexane and methylcyclopentane from light naphtha feedstock.The feed of C₆ raffinate stream contains paraffin and cycloparaffins.Benzene saturated hydrocarbon stream is fed to fractional distillationto separate the mixture of cyclohexane and heptanes at the bottom of thecolumn and mixture of methylcyclopentane and n-hexane at the top of thecolumn. Then the both streams processes through extractive distillationseparately. In an extractive distillation column, solvent is added whichseparates the components by changing the relative volatilities of thecomponents of the mixture and effective separation by distillationbecomes possible. The solvent for extractive distillation is chosen onthe basis of solubility and comparable Hansen dispersive force as thatof component to be separated to cause great differences between therelative volatilities of the components in a mixture and ease theseparation with fewer distillation stages, lower amount of reflux andhigher product purity.

Accordingly, in another preferred embodiment, the present inventionprovides a process for producing pure n-hexane, said process comprising:

-   -   (a) subjecting a benzene saturated hydrocarbon stream to        fractional separation at a temperature in range of 65° C. to        100° C. to split the benzene saturated hydrocarbon stream into a        bottom stream comprising a mixture of cyclohexane and        iso-heptane and a top stream comprising a mixture of        methylcyclopentane (MCP) and n-hexane;    -   (b) subjecting the top stream of step (a) to extractive        distillation to obtain n-hexane and methylcyclopentane by using        an organic solvent; and    -   (c) separating pure n-hexane.

In other embodiment, after benzene saturation, the hydrocarbon feed(i.e. saturated light naphtha feedstock) contains predominantlycyclohexane, methylcyclopentane and paraffins like n-hexane andiso-heptanes with benzene less <100 ppm. The minimum boiling point offeed should not be less than 65 and should not be more than 100.

In another embodiment, the extractive distillation of top stream furthercomprises of:

-   -   (a) subjecting a feed containing top stream comprising        methylcyclopentane and n-hexane to the extractive distillation;    -   (b) separating n-hexane rich stream and methylcyclopentane rich        stream from the feed of step (a) by addition of an organic        solvent wherein the solvent to the feed ratio is 3% vol/vol;    -   (c) isolating the n-hexane rich stream and a methylcyclopentane        rich stream containing organic solvent separately;    -   (d) partially condensing the n-hexane rich stream of step (c) to        obtain pure n-hexane; and    -   (e) separating the organic solvent from the methylcyclopentane        rich stream of step (c) to obtain pure methylcyclopentane.

In one another embodiment, a portion of condensed stream of n-hexaneobtained from step (d) is returned back as a reflux for the extractivedistillation.

In one another embodiment, the organic solvent obtained from step (e) isrecycled back to step (b) for separation of the n-hexane rich stream andmethylcyclopentane rich stream from the feed.

In a preferred embodiment, the organic solvent is selected frommonoethylene glycol (MEG), triethylene glycol (N-methyl pyrrolidone(NMP), sulfolane and dimethyl sulfoxide (DMSO) and most preferably fromMEG and TEG.

In another embodiment, the extractive distillation of the bottom streamof step (b) comprises steps of:

-   -   (a) subjecting a feed containing bottom stream comprising a        mixture of cyclohexane and iso-heptane to extractive        distillation;    -   (b) separating iso-heptane rich stream and cyclohexane rich        stream from the feed of step (a) by addition of an organic        solvent wherein the solvent to the feed ratio is 3% vol/vol;    -   (c) isolating the iso-heptane rich stream and a cyclohexane rich        stream containing organic solvent separately;    -   (d) partially condensing the iso-heptane rich stream of step (c)        to obtain pure iso-heptane; and    -   (e) separating the organic solvent from the cyclohexane rich        stream of step (c) to obtain pure cyclohexane.

In further embodiment, a portion of condensed stream of iso-heptaneobtained from step (d) is returned back as a reflux for the extractivedistillation.

Also, the organic solvent obtained from step (e) is recycled back tostep (b) for separation of the iso-heptane rich stream and cyclohexanerich stream from the feed.

The feed mixture comprising C₆ raffinate hydrocarbons and para-xyleneraffinate is benzene saturated where benzene is converted intocyclohexane. The benzene saturated hydrocarbon stream thus obtained issent to fractionators [4] through conduit [1] for splitting into twostreams to cyclohexane rich bottom stream through conduit [6] and MCPrich stream through conduit [5] respectively. The lighter fractions [2](having hydrocarbon with carbon atoms less than C₆) and the heavierfractions [3] (having hydrocarbon with carbon atoms more than C₆) areseparated from the fractionator [4].

Extractive Distillation:

The MCP rich stream containing n-hexane conduit [5] is then fed toextractive distillation column [8] where the Solvent from solventstorage [29] is introduced to extractive distillation column [8] throughconduit [10], and an overhead stream enriched in High purity hexane iswithdrawn from an upper portion of distillation column [8] throughconduit [11]. This overhead stream can be partially condensed, with aportion thereof being returned to the fractionation zone as reflux. Theoverhead stream passing through conduit [11] is condensed in condenser[31] to yield a condensed overhead stream. A portion of the condensedoverhead stream can be returned to distillation column [8] as refluxthrough conduit [17], while the remainder of the condensed overheadstream is yielded as a High purity hexane through conduit [21].

A bottoms stream of extractive distillation column [8] rich with MCP iswithdrawn from a lower portion of the extractive distillation column [8]through conduit [13]. A portion of the fluids withdrawn from the bottomof extractive distillation column [8] may be heated in reboiler [32] andthen passed back to a lower portion of extractive distillation column[8] through conduit [19]. The feed mixture introduced into extractivedistillation column [8] will be fractionated to yield an overhead streamwhich is enriched in High purity hexane and a bottoms streampredominantly comprising the MCP and the solvent.

The bottoms stream passing through conduit [13] is passed todistillation column [15]. Differences in the boiling point andadjustment of the temperature in the distillation column, the bottomsstream passing through conduit [13] can be easily fractionated intosolvent stream [33]. An overhead stream predominantly comprising MCP iswithdrawn from an upper portion of distillation column [15] throughconduit [23]. This overhead stream can be at least partially condensedin condenser [34]. A portion of the overhead stream withdrawn fromcondenser [34] can be returned through conduit [25] as reflux for MCPthrough conduit [25].

A bottoms stream mainly comprising the solvent is withdrawn from a lowerportion of distillation column [15] through conduit [33]. A portion ofthis bottoms stream is preferably routed back to solvent stream [29] andthen recycled to extractive distillation column [8], while anotherportion of the bottoms stream is heated in a reboiler [35] and returnedto the lower portion of column [15]. Solvent lost during processing ismade up by a makeup stream passing through conduit [33] and solventstream [29].

The cyclohexane rich stream conduit [6] is then fed to extractivedistillation column [7] where the Solvent from solvent storage [30] isintroduced to extractive distillation column [7] through conduit [9],and an overhead stream enriched in iso-heptanes is withdrawn from anupper portion of distillation column [7] through conduit [12]. Thisoverhead stream can be partially, with a portion thereof being returnedto the fractionation zone as reflux. The overhead stream passing throughconduit [12] is condensed in condenser [36] to yield a condensedoverhead stream. A portion of the condensed overhead stream can bereturned to distillation column [7] as reflux through conduit [18],while the remainder of the condensed overhead stream is yielded as aproduct through conduit [22].

A bottom stream of extractive distillation column [7] rich withcyclohexane is withdrawn from a lower portion of the extractivedistillation column [7] through conduit [14]. A portion of the fluidswithdrawn from the bottom of distillation column [14] may be heated inreboiler [37] and then passed back to a lower portion of distillationcolumn [7] through conduit [20].

The feed mixture introduced into extractive distillation column [7] willbe fractionated to yield an overhead stream which is enriched in Highpurity hexane and a bottoms stream predominantly comprising thecyclohexane and the solvent.

The bottom stream passing through conduit [14] is passed to distillationcolumn [16]. Differences in the boiling point and adjustment of thetemperature in the distillation column, the bottoms stream passingthrough conduit [14] can be easily fractionated into solvent stream[38]. An overhead stream predominantly comprising cyclohexane iswithdrawn from an upper portion of distillation column [16] throughconduit [24]. This overhead stream can be at least partially condensedin condenser [39]. A portion of the overhead stream withdrawn fromcondenser [39] can be returned through conduit [26] as reflux fordistillation column [16], with the remainder of the overhead streambeing withdrawn as product, i.e., cyclohexane through conduit [26].

A bottom stream predominantly comprising the solvent is withdrawn from alower portion of distillation column [16] through conduit [38]. Aportion of this bottoms stream is preferably routed back to solventstream [30] and then recycled to extractive distillation column [7],while another portion of the bottoms stream is heated in a reboiler [40]and returned to the lower portion of column [16]. Solvent lost duringprocessing losses can be made up by a makeup stream passing throughconduit [38] and solvent stream [30].

Accordingly, in another embodiment, the present invention relates to anapparatus for producing pure n-hexane wherein said apparatus comprising:

-   -   (a) a fractional distillation unit [4] to split a benzene        saturated hydrocarbon stream into a bottom stream comprising        cyclohexane and iso-heptane, and a top stream comprising        methylcyclopentane (MCP) and n-hexane;    -   (b) an extractive distillation column [8] for fractionating the        top stream into an overhead stream rich in n-hexane and a bottom        stream comprising methylcyclopentane and organic solvent;    -   (c) a solvent storage [29] for introducing solvent to the        extractive distillation column [8];    -   (d) a condenser [31] for condensing pure n-hexane stream wherein        a portion of condensed stream is passed to the extractive        distillation column [8] through a conduit [17]; and    -   (e) a conduit [21] for isolating pure n-hexane.

In another embodiment of the present invention, the apparatus of thepresent invention further comprises of:

-   -   (a) a distillation column [15] for separating pure        methylcyclopentane stream and organic solvent;    -   (b) a condenser [34] for condensing the pure methylcyclopentane        stream wherein a portion of condensed methylcyclopentane stream        is returned to the distillation column [15] as a reflux through        conduit [25] and remaining is isolated through conduit [25];    -   (c) a conduit [33] for transferring a portion of organic solvent        from the distillation column [15] to the solvent storage [29];        and    -   (d) a reboiler [35] for heating a portion of the organic solvent        and returning the hot organic solvent to the bottom of the        distillation column [15].

In one another embodiment, the apparatus of the present inventionfurther comprises of:

-   -   (a) an extractive distillation column [7] for fractionating        overhead iso-heptane rich stream and a bottom stream comprising        cyclohexane and organic solvent;    -   (b) a solvent storage [30] for introducing solvent to the        extractive distillation column [7];    -   (c) a condenser [36] for condensing the overhead iso-heptane        stream wherein a portion of condensed stream is returned to the        extractive distillation column [7] as a reflux through a conduit        [18];    -   (d) a conduit [22] for isolating pure iso-heptane.

In one another embodiment of the present invention, the apparatus of thepresent invention further comprises of:

-   -   (a) a distillation column [16] for fractionating cyclohexane and        organic solvent wherein isolating pure cyclohexane stream from        top of the distillation column [16] and organic solvent from        bottom of the distillation column [16];    -   (b) a condenser [39] for condensing the pure cyclohexane stream        wherein a portion of condensed cyclohexane stream is returned to        the distillation column [16] through conduit [26] and remaining        is isolated through conduit [26];    -   (c) a conduit [38] for transferring a portion of organic solvent        from the distillation column [16] to the solvent storage [30];        and    -   (d) a reboiler [40] for heating a portion of the organic solvent        and returning the hot organic solvent to the bottom of the        distillation column [16].

In further embodiment, the process of the present invention optionallycomprises of a step wherein a portion of the fluids withdrawn from thebottom of the extractive distillation column [8] may be heated inreboiler [32] and then passed back to a lower portion of extractivedistillation column [8] through conduit [19].

Example 1

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methylcyclopentane with MEG as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase n-Hexane % 69.1 58.23 72.41Methylcyclopentane, % 30.9 41.77 27.59

The separation factor in the above example has been found to be 1.88

Example 2

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with TEG as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase n-Hexane % 87.91 93.61 86.48Methylcyclopentane, % 12.09 6.93 13.51

The separation factor in the above example has been found to be 2.29

Example 3

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with NMP as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase n-Hexane % 90.51 89.78 97.10Methylcyclopentane, % 9.49 10.22 2.90

The separation factor in the above example has been found to be 3.81

Example 4

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with Sulfolane as a solvent. Thesolvent-to feed ratio was 3 vol/vol. The mixture of solvent and feedwere heated to a temperature of 75° C. and the vapors were condensed andcompletely refluxed back to the solvent feed mixture. After 2 hours ofdistillation and total reflux, samples of both liquid and condensedvapor were collected and analyzed for composition. The results aresummarized in the following table:

Liquid Feed Phase Vapor Phase n-Hexane % 89.56 89.10 91.70Methylcyclopentane, % 10.44 10.90 8.30

The separation factor in the above example has been found to be 1.35

Example 5

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with DMSO as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase n-Hexane % 89.02 89.77 90.05Methylcyclopentane, % 10.18 10.23 9.95

The separation factor in the above example has been found to be 1.03

Example 6

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with MEG as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase Methylcyclopentane, % 98.24 99.57 97.78n-Hexane, % 1.73 0.43 2.22

The separation factor in the above example has been found to be 5.25

Example 7

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with NMP as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase Methylcyclopentane, % 0.74 0.82 0.37n-Hexane, % 99.26 99.18 99.63

The separation factor in the above example has been found to be 2.22

Example 8

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with NMP as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase Methylcyclopentane, % 90.45 91.35 82.81n-Hexane, % 9.55 8.65 17.19

The separation factor in the above example has been found to be 2.19

Example 9

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with Sulfolane as a solvent. Thesolvent-to feed ratio was 3 vol/vol. The mixture of solvent and feedwere heated to a temperature of 75° C. and the vapors were condensed andcompletely refluxed back to the solvent feed mixture. After 2 hours ofdistillation and total reflux, samples of both liquid and condensedvapor were collected and analyzed for composition. The results aresummarized in the following table.

Liquid Feed Phase Vapor Phase Methylcyclopentane, % 89.03 88.55 91.27n-Hexane, % 10.97 11.44 8.73

The separation factor in the above example has been found to be 0.74

Example 10

Experiments were conducted with hydrocarbon feedstock consisting ofhexane and methyl cyclopentane with DMSO as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 75° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Liquid Feed Phase Vapor Phase Methylcyclopentane, % 87.54 86.81 91.04n-Hexane, % 12.45 13.19 12.45

The separation factor in the above example has been found to be 0.647

The data summarized in Table II indicates that for separation of hexanefrom MCP for the production of high purity n-hexane, MEG, TEG and NMPacts as a better solvent compare to DMSO and Sulfolane.

TABLE II LIQUID FEED FRACTION VAPOR (%) (%) FRACTION (%) Sep SOLVENT MCPHEXANE MCP HEXANE MCP HEXANE S/F Factor MEG 69.1 30.9 58.23 41.77 72.4127.59 3 1.88 TEG 12.09 87.91 6.93 93.61 13.51 86.48 3 2.29 NMP 9.4990.51 10.21 89.79 2.89 97.10 3 3.81 SULFOLANE 10.44 89.56 10.89 89.108.30 91.70 3 1.35 DMSO 10.18 89.02 10.23 89.77 9.94 90.05 3 1.03 MEG98.24 1.73 99.57 0.43 97.78 2.22 3 5.25 NMP 0.74 99.26 0.82 99.18 0.3799.63 3 2.22 NMP 90.45 9.55 91.35 8.65 82.81 17.19 3 2.19 SULFOLANE89.03 10.97 88.55 11.44 91.27 8.73 3 0.74 DMSO 87.54 12.45 86.81 13.1991.04 8.96 3 0.64 *S/F is solvent to feed ratio

Example 11

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptane with MEG as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 84.59 85.87 83.97 Iso-heptanes15.41 14.13 16.03

The separation factor in the above example has been found to be 1.16

Example 12

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptanes with MEG as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 98.98 99.3 98.35 Iso-heptanes1.02 0.7 1.65

The separation factor in the above example has been found to be 2.37.

Example 13

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptanes with NMP as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 90.09 90.41 87.28 Iso-heptanes9.91 9.59 12.72

The separation factor in the above example has been found to be 1.37.

Example 14

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptanes with NMP as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 97.17 99.32 98.48 Iso-heptanes0.83 0.67 1.51

The separation factor in the above example has been found to be 2.25.

Example 15

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptanes with DMSO as a solvent. The solvent-to feedratio was 3 vol/vol. The mixture of solvent and feed were heated to atemperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 90.45 90.69 89.29 Iso-heptanes9.55 9.30 10.71

The separation factor in the above example has been found to be 1.17.

Example 16

Experiments were conducted with hydrocarbon feedstock consisting ofcyclohexane and iso-heptanes with Sulfolane as a solvent. The solvent-tofeed ratio was 3 vol/vol. The mixture of solvent and feed were heated toa temperature of 80° C. and the vapors were condensed and completelyrefluxed back to the solvent feed mixture. After 2 hours of distillationand total reflux, samples of both liquid and condensed vapor werecollected and analyzed for composition. The results are summarized inthe following table.

Feed Liquid Phase Vapor Phase Cyclohexane 89.50 89.67 87.77 Iso-heptanes10.59 10.33 12.22

The separation factor in the above example has been found to be 0.826.

The data summarized in Table III indicates that for separation ofCyclohexane from iso-heptane, MEG, TEG and NMP are better solventcompare to DMSO and Sulfolane

TABLE III LIQUID VAPOR FEED FRACTION FRACTION (%) (%) (%) Sep SOLVENTChex i-hep Chex i-hep Chex i-hep S/F Factor MEG 84.59 15.41 85.87 14.1383.97 16.03 3 1.16 TEG 98.98 1.02 99.3 0.7 98.35 1.65 3 2.37 NMP 90.099.91 90.41 9.59 87.28 12.72 3 1.37 NMP 99.17 0.83 99.32 0.68 98.48 1.513 2.25 SULFOLANE 89.50 10.59 89.67 10.33 87.77 12.22 3 0.826 DMSO 90.459.55 90.69 9.31 89.29 10.71 3 1.17

Simulation studies were also carried out with Aspen to simulate the flowscheme given in FIG. 1. Studies were done to determine the number oftheoretical stage that are required in each column of extractivedistillation and recovery of solvent and recycle. The result indicatedthat the cyclohexane is recovered at the bottom of column [8] along withthe solvent and solvent free iso-heptane at the top of same column.Methylcyclopentane with solvent and solvent free High purity n-hexane(also referred as hexane) is also recovered at the bottom and top ofcolumn [7] respectively. The simulation also confirmed that the solventcan be recovered and recycled. After solvent recovery, solvent freecyclohexane and methylcyclopentane are recovered in column [16] and [15]respectively. The simulation results were in line with the experimentaldata and validated the experiment findings.

Accordingly, the present invention relates to a process which is usefulfor isolation of pure methylcyclopentane, pure iso-heptane and purecyclohexane along with the pure n-hexane.

The invention claimed is:
 1. A process for producing n-hexane, saidprocess comprising: (a) subjecting a benzene saturated hydrocarbonstream to fractional separation at a temperature in range of 65° C. to100° C. to split the benzene saturated hydrocarbon stream into a topstream and a bottom stream, wherein the bottom stream comprises amixture of cyclohexane and iso-heptane and the top stream comprises amixture of methylcyclopentane (MCP) and n-hexane; (b) subjecting the topstream of step (a) to extractive distillation to obtain n-hexane andmethylcyclopentane by using an organic solvent; and (c) separatingn-hexane.
 2. The process as claimed in claim 1, wherein the extractivedistillation of said top stream of step (a) further comprises steps of:(a) subjecting a feed containing the top steam comprisingmethylcyclopentane and n-hexane to the extractive distillation; (b)separating a n-hexane rich stream and a methylcyclopentane rich streamfrom the feed of step (a) by addition of an organic solvent wherein thesolvent to the feed ratio is 3% vol/vol; (c) isolating the n-hexane richstream and the methylcyclopentane rich stream containing organic solventseparately; (d) partially condensing the n-hexane rich stream of step(c) to obtain a condensed stream comprising n-hexane; and (e) separatingthe organic solvent from the methyl cyclopentane rich stream of step (c)to obtain methylcyclopentane.
 3. The process as claimed in claim 2,wherein a portion of the condensed stream of n-hexane obtained from step(d) is returned back as a reflux for the extractive distillation.
 4. Theprocess as claimed in claim 2, wherein the organic solvent obtained fromstep (e) is recycled back to step (b) for separation of the n-hexanerich stream and methylcyclopentane rich stream from the feed.
 5. Theprocess as claimed in claim 2, wherein the organic solvent is selectedfrom monoethylene glycol (MEG), triethylene glycol (TEG), N-methylpyrrolidone (NMP), sulfolane and dimethyl sulfoxide (DMSO).
 6. Theprocess as claimed in claim 1, wherein the extractive distillation ofthe bottom stream of step (b) comprises steps of: (a) subjecting a feedcontaining the bottom stream comprising a mixture of cyclohexane andiso-heptane to extractive distillation; (b) separating an iso-heptanerich stream and a cyclohexane rich stream from the feed of step (a) byaddition of an organic solvent wherein the solvent to the feed ratio is3% vol/vol; (c) isolating the iso-heptane rich stream and thecyclohexane rich stream containing organic solvent separately; (d)partially condensing the iso-heptane rich stream of step (c) to obtainisoheptane; and (e) separating the organic solvent from the cyclohexanerich stream of step (c) to obtain cyclohexane.
 7. The process as claimedin claim 6, wherein a portion of condensed stream of iso-heptaneobtained from step (d) is returned back as a reflux for the extractivedistillation.
 8. The process as claimed in claim 6, wherein the organicsolvent is selected from monoethylene glycol (MEG), triethylene glycol(TEG), N-methyl pyrrolidone (NMP), sulfolane and dimethyl sulfoxide(DMSO).
 9. The process as claimed in claim 6, wherein the organicsolvent obtained from step (e) is recycled back to step (b) forseparation of the iso-heptane rich stream and cyclohexane rich streamfrom the feed.
 10. The process as claimed in claim 1, wherein theprocess is further used for isolation of methylcyclopentane, iso-heptaneand cyclohexane along with the n-hexane.